1. Field of the Invention
The present invention relates to pumps, and more particularly, to regenerative type pumps, which are also known as Wesco pumps.
2. Description of the Related Art
An example of a regenerative type pump is disclosed in Japanese Laid-Open Patent Publication No. 3-18688 and has an impeller rotatably disposed within a pump casing. The pump casing has an inlet port and a discharge port, both of which are fixed in position on opposite sides of the impeller. A plurality of blade grooves are formed along the perimeter of the impeller. Fluid is drawn through the inlet port by the impeller and discharged through the discharge port along a travelling path of the impeller blade grooves. The upper portion of the pump casing has a groove beginning with a groove inlet portion and ending with the discharge port. A partition is formed between the groove inlet portion and the discharge port and the partition forms a terminal end of the fluid path within the pump casing.
In such a regenerative type pump, if some of the high-pressure fluid collides with the terminal end of the fuel path without being smoothly discharged through the discharge port, high frequency noise is generated.
In order to reduce such noise in the terminal end of the fluid path, Japanese Laid-Open Patent Publication No. 6-288381 discloses a regenerative type pump in which an opening end face of the discharge port that faces the impeller has an opening width that gradually decreases along the direction of rotation of the impeller. In this publication, the inventors allege that fluid will smoothly pass through the passage and gradually contact a wall surface that defines the opening end face having the gradually tapered opening. Therefore, the inventors stated that noises caused by such collisions are reduced. However, based upon experiments performed by the Applicant, even in this regenerative type pump, some of the high-pressure fluid still collides with the terminal end passage on the downstream side of the discharge port. Therefore, this known pump does not significantly reduce noise generated in the termination of the fluid passage.
It is, accordingly, an object of the present invention to teach improved regenerative type pumps. Preferably, such improved regenerative type pumps generate less noise than known pumps.
In one aspect of the present teachings, regenerative type pumps are constructed such that the fluid is smoothly discharged from the discharge port and the amount of high-pressure fluid that collides against the terminal end of the discharge port is minimized.
In another aspect of the present teachings, a groove of substantially constant width is circumferently formed within an inner pump cover on the side of the inner pump cover that faces the impeller. The groove begins with a groove inlet portion, ends with the discharge port and a partition is disposed between the groove inlet portion and the discharge port.
Preferably, the opening portion of the discharge port has a tapered portion and a damping portion. The tapered portion has an opening width that gradually decreases in the circumferential direction. The damping portion is contiguous with the tapered portion and has an opening width that is substantially constant in the circumferential direction. This design allows high-pressure fluid to be smoothly delivered to and discharged from the discharge port. Therefore, the amount of high-pressure fluid that collides with the terminal end of the discharge port is decreased and pump noise can be reduced.
A corner portion may exist between the wall surfaces of the tapered portion and the damping portion of the discharge port and a lower surface of the inner pump cover. In one embodiment, this corner portion is chamfered to permit fluid to smoothly flow from the tapered portion to the damping portion. As a result, the fluid flow rate is not abruptly decreased in the terminal end of the tapered portion and pump noise can be further reduced.
A front wall surface of the discharge port, which can be disposed forward in the direction of rotation of the impeller, preferably includes an oblique surface that forms an acute angle with the lower surface of the inner pump cover. Thus, the fluid can smoothly flow into the discharge port along the oblique surface, so that the pump efficiency can be enhanced. Further, the discharge port can be easily manufactured by injection molding, due to the oblique configuration of the front wall surface of the discharge port.
Further, a rear wall surface may be located in the discharge port and rearward in the direction of rotation of the impeller. This rear wall surface preferably includes an oblique surface that forms an acute angle with the lower surface of the inner pump cover. Thus, the fluid can smoothly flow into the discharge port, so that the pump efficiency can be enhanced.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.